1. Field of the Invention
The present invention relates to an inhalation apparatus that discharges an agent such as medicine, fragrance, or nicotine so that the user can inhale it.
2. Description of the Related Art
A method for dosing using an inhalation apparatus is known. Unlike an injection, such dosing through the respiratory system does not cause pain. Such an inhalation apparatus can also serve as a portable terminal including a storage unit that stores information on the user including the user's medical record and prescription, and a discharge device that discharges an agent in the form of minute droplets so that the user can inhale them. Such an inhalation apparatus can also include a discharge control unit that makes the discharge device discharge the agent according to the user's inhalation profile so that the user can inhale the agent according to the prescription information (see WO95/01137 and WO02/04043).
In inhalation apparatuses, it is necessary to accurately control the dose of the agent. The diameter of agent droplets is important to accurately control the dose. The diameter of agent droplets at the suction port through which the user inhales affects the amount of agent that reaches the user's lungs. That is, if the amount of agent discharged from an inhalation apparatus is constant but the diameter of agent droplets is larger or smaller than the optimum value, the amount of agent that the user can inhale decreases. Specifically, droplets having a diameter of around 3 μm can reach the user's alveoli. Droplets having a diameter larger than around 3 μm cannot reach the user's alveoli and are deposited in the user's bronchi, for example. It is known that droplets having a diameter smaller than around 3 μm are not absorbed into the user's body and are discharged by exhalation. However, in the case where an agent is discharged in the form of minute droplets, the diameter of droplets changes due to evaporation.
The amount of evaporation fluctuates with changes in the surrounding environment, for example, factors such as temperature and humidity. Therefore, it is difficult to keep the diameter of agent droplets at the optimum value. As a result, the amount of agent that the user inhales cannot be accurately controlled. Therefore, an inhalation apparatus in which a constant droplet diameter can be obtained regardless of use environment is desirable.
As a solution to this problem, WO96/009846 discloses an inhaler that functions to accelerate evaporation using a heater and a dehumidifier so as to make the droplet diameter constant. This document also describes saturating inhaled air with water vapor so as to prevent evaporation of droplets.
However, the configuration disclosed in the above document requires a heater or a dehumidifier that accelerates evaporation to control the change in droplet diameter due to evaporation. Located inside the airflow path, it can interfere with the inhalation airflow and therefore can interfere with ease of inhalation of the user. There is no description of a specific water-vapor generator, including the position where the generator is located.
In the case where the discharged agent does not spread throughout the airflow path, it is not necessary to make the entire airflow path an evaporation-controlled environment. This leads to wasteful consumption of energy in the inhalation apparatus and an increase in weight and size of the inhalation apparatus, and consequently degrades the portability of the inhalation apparatus.